Palladium–Magnesium Oxide Nanocatalyst for Selective Hydrogenation: Enhancing Naphtha Stability and Biodiesel Performance

B. S. Aziz, J. S. Aziz, H. H. Mohammed and R. Z. Homod

Abstract
The hydrogenation of naphtha is critical to producing stable, clean gasoline, yet current catalysts often lack selectivity and stability. In this work, a novel palladium–magnesium oxide (Pd/MgO) nanocatalyst was developed to address these challenges. The catalyst was prepared by reduction of Na2PdCl4 on MgO support using sodium borohydride, resulting in well-dispersed Pd nanoparticles with an average size of 1.7 nm and a Pd loading of 0.9 wt.% (nominally 1 wt.%). The size, composition, and dispersion of the nanoparticles were confirmed using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen pulse chemisorption, inductively coupled plasma atomic emission spectroscopy, and hydrogen temperature programmed reduction measurements. Catalytic tests showed great activity of quinoline hydrogenation at 150 °C and 40 atm H₂, with a corrected turnover frequency (TOFcorr) of 6400 h⁻¹, which was almost fourfold higher than Pd/SiO₂ and Pd/Al₂O₃ commercial catalysts (TOFcorr = 1600-1800 h⁻¹). Linear alkenes were hydrogenated with the catalyst at mild conditions (25 °C and 10 atm H₂). Moreover, during biodiesel upgrading, the conversion of polyunsaturated fatty acid methyl esters to stable monounsaturated products was achieved at (100 °C, 1 atm of H₂ with >80 % conversion). Recyclability tests proved that the alkene hydrogenation activity was stable in three cycles, and only slight deactivation in quinoline hydrogenation occurred. This work shows that the Pd/MgO nanocatalysts are promising for enhancing the quality of gasoline, minimizing the formation of gums, and increasing the stability of biodiesel because of their nanoscale dispersion, high selectivity, and recyclability.

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Keywords
naphtha hydrogenation , palladium nanocatalyst (Pd NPs), selective hydrogenation